1. Field of the Invention
The present invention relates to a fluid-structure coupled numerical simulation method and a program for a fluid-structure coupled numerical simulation storage device. Particularly, the present invention relates to the aforementioned method and program, in which when applying a fluid to a film structure, assuming that a film surface is a surface of a fixed area in a computational mesh, a fluid analysis is executed in the same solver with respect to the relationship between a repulsive force of the film surface of the film structure and a fluid pressure.
2. Description of the Related Art
In the past, when simulating physical action of a design model, for example, conducting a thermal conductivity analysis, fluid analysis, structural analysis, electromagnetic field analysis, electromagnetic wave analysis and the like by a computer to verify the design model, a coupled analysis in which two or more kinds of simulation are applied is performed on an object model, corresponding to the object model for analysis being complicated.
In such coupled analysis, it is necessary to set a plurality of physical parameters for element groups if two or more physical models are provided, and so work of setting becomes complicated when one-dimensional list is used. Further, when boundary conditions are set, it is necessary to perform the setting while considering a setting condition for each of the element groups, that is, which boundary corresponds to which physical model, thereby bringing the complexity to the work. Japanese Patent Application Publication No. 2002-245097 discloses a coupled analysis method of easily setting conditions on element groups and boundaries regarding an object model, a method of setting the analysis conditions, a storage device and program in a coupled analysis system using two or more physical models.
FIG. 1 shows the coupled analysis system disclosed in the above-mentioned patent reference configured to have a CPU (Central Processing Unit) 1, display 2, input device 3 such as a mouse and filing device (storage device) 4. The CPU 1 implements CAD model preparation processing 10 by which a model to which a numerical simulation is implemented is prepared. The prepared model is divided into mesh (elements), and at this time, mesh preparation processing 11 that defines a group and boundary of each mesh is implemented. Groups are registered in a group list 6, boundaries are registered in a boundary list 7, and the corresponding relations between groups and boundaries are registered in a corresponding list 5. As shown in FIG. 1, the corresponding list 5 is provided in the filing device 4. List-registration processing 12 that stores group numbers and corresponding boundary numbers is performed, and analysis conditions with respect to the groups and boundaries of the meshes (elements) divided are set by element group analysis-condition-setting processing 13 and element boundary analysis-condition-setting processing 14. For example, thermal conductivity is set to the element groups and a temperature and thermal conductivity are set to the boundaries in the thermal conductivity analysis. Further, a young's modulus or the like is set to the element groups and a weight condition or the like is set to the boundaries in the structural analysis. Both the analysis-condition-setting processings 13 and 14 are linked mutually.
Subsequently, physical-model simulation/computation processing 15 and computed-result display processing 16 are implemented. Here, computation is implemented in the computation processing 15 using the model divided into mesh and analysis conditions, thereby obtaining a solution. A general-purpose thermal analysis program, structural analysis program and fluid analysis program are used in the computation processing 15. The result display processing 16 is performed such that the computed result obtained by the computation processing is output to a screen of a display 2. As described above, the CPU performs such steps 10 and 11 of setting physical models of the element groups constituting the object model, and step 12 of retrieving boundaries of the object model corresponding to the element groups that were set. Further, the CPU performs a step 13 of reflecting the physical models of the element groups to the retrieved boundaries on analysis-condition-setting screen for the boundaries of the object model, and a step 14 of setting analysis conditions of the boundaries on the analysis-conditions-setting screen for the boundaries reflected. By using a principle of a specific group and the boundary thereof having a common physical-model characteristic, correlation between the group and boundary is reflected on a boundary condition setting screen, and the physical model of the group is set to automatically retrieve the boundary corresponding to the group, and the analysis conditions of the boundary are set on the boundary condition-setting screen.
As described above, the technology described in Japanese Patent Application Publication No. 2002-245097 includes the function of displaying a two-dimensional list of the physical models (thermal conductivity, fluid, structural analysis, static electromagnetic field and electromagnetic field) and names of the boundaries. Therefore, referencing the corresponding list 5 in the filing device 4, a situation in which the physical model of each element group is assigned is displayed on the boundary list and boundaries to which the conditions-setting in the boundaries list are needed are automatically checked. For example, a checked result is displayed with a circle or the like, and so the setting of the boundary condition of the physical model to which each boundary corresponds can be performed by clicking (or double clicking) an area of the boundary name checked. Accordingly, since the two-dimensional list is prepared as described above, the setting of physical parameters to the element groups becomes easy in an achievement analysis having a plurality of physical models. Further, situations of the physical parameters set to the element groups are determined, the boundary condition to which setting is needed is automatically checked, and can be set in the boundary list, thereby the setting of boundary conditions being facilitated. Furthermore, the element group list, boundary list and shapes of models can be output simultaneously, thus facilitating understanding of the setting conditions for analysis.
Japanese Patent Application Publication No. 2000-271734 discloses a fluid-solidification analysis method to which computer simulation is applied. This method is to find an optimal method and optimal condition for producing a high quality product without casting defects such as a flow defect caused by the decrease in temperature in a molten metal flow, in the case where metal melt material is used as fluid to form cast or die-cast products.
The state of molten metal solidified is modeled with a solid-phase rate which shows a rate of the solid phase existing in the liquid phase based on the temperature of each minute element. The molten metal is treated as Newtonian fluid in the state of the solid-phase rate of 0% at a temperature higher than the liquidous line temperature, is treated as non-Newtonian fluid in the solid-liquid co-existent area at a temperature higher than the solidus line temperature and lower than the liquidous line temperature, and is treated as the obstacle not fluid in the state of the solid-phase rate of 100% at a temperature lower than the solidus line temperature. Thus, an optimum flow-field analysis method is applied to each solidified state, enabling an analysis result with high accuracy for the process to be practically obtained in a short period of time.
FIG. 2 shows a flow chart of the fluid-solidification analysis method to which the computer simulation described in the above-described patent reference is applied. In order to implement the fluid-solidification analysis of molten metal inside a mold, a shape model is prepared based on a molded product by injection molding and the mold used for the injection molding in step S1. An analysis shape model divided into minute elements is prepared using mesh in step S2. The analysis model is suitable for a difference method, finite element method, boundary element method, FAN method, control volume method and the like that are fluid-solidification analysis methods.
In step S3, input condition data such as physical property data, boundary conditions, process conditions and the like necessary for the fluid-solidification analysis after preparing the analysis shape model are determined and input. Hereupon, the input condition data are set for simulating a process that produces a molded product by the numerical analysis with respect to the analysis shape model. Those are conditions necessary for the analysis, such as a inflow velocity of molten metal, inflow temperature and filling time, mold temperature, values of dynamic physical properties and thermal physical properties of the mold, values of dynamic physical properties and thermal physical properties of the molten material, boundary conditions (such as thermal boundary condition) and the like.
In the next step S4, a process in which the molten metal is filled inside the mold is simulated using a numerical analysis method on the basis of the given input condition data. When implementing the analysis, the solidified state of molten metal in each minute element is modeled using the solid-phase rate that shows a rate of solid phase existing in the liquid phase from the temperature of each minute element, and a state of the molten metal is determined. Specifically, as shown in step S5, the state of the molten metal, which is the complete liquid-phase state, solid-liquid co-existing state or complete solid-phase state, is determined from the temperature of the molten metal. The complete liquid-phase state is the range at a temperature higher than the liquidous line temperature and the solid-phase rate is 0%. The solid-liquid co-existent state is the range at a temperature higher than solidus line temperature and lower than liquidous line temperature. The complete solid-phase state is the range at the temperature lower than solidus line temperature and the solid-phase rate is 100%.
After the state is determined, an optimal flow-field analysis method is applied to each solidified state based on the state determined, and the simulation is implemented using the numerical analysis method to conduct a flow analysis. The flow analysis employing the numerical analysis method is implemented at predetermined time intervals in accordance with the input condition data and the solid-phase rate. Here, the predetermined time interval is an interval in the range of about 0.001 to 0.01 sec. When implementing the flow analysis to the state in which the molten metal in each minute element is in the solid-phase rate of 0% at the temperature higher than the liquidous line temperature, the flow analysis is implemented regarding the molten metal as Newtonian fluid. Further, in the state in which the molten metal in each minute element is in the solid-liquid coexistent range at the temperature higher than the solidus line temperature and lower than the liquidous line temperature, the flow analysis is implemented regarding the molten metal as non-Newtonian fluid. Furthermore, in the state in which the molten metal in each minute element is in the solid-phase rate of 100% at the temperature lower than the solidus line temperature, the molten metal is treated as the obstacle instead of fluid and the flow analysis is not implemented.
After the fluid analysis, in order for the filling state of molten metal in the mold being changed by the result of the fluid analysis to be reflected in temperature distribution, temperature analysis is implemented in step S6 regarding temperature changed situations of the molten metal and mold using the numerical analysis method at predetermined time intervals of about 0.01 to 0.02 sec. After the temperature analysis, whether to continue the analysis is judged from the given input condition data, and in the case of “NO”, operation goes back to the step S4, and in the case of “YES”, operation proceeds to step S8 to end. Further, positions such as flow defect portions where defects may occur are predicted in step S8 based on the analysis result obtained in step S7 indicating molten metal unfilled portions.
If the occurrence of defects are predicted in step S8, as shown in step S9, at least one of the conditions of the analysis shape model and input condition data is changed and each of process from the step S1 to step S8 is repeated until it is recognized that the occurrence of defects is not predicted. Then, the processing ends when the occurrence of defects is not predicted in the step S8.
As described above, Japanese Patent Application Publication No. 2002-245097 discloses the technology to simplify settings of boundary conditions that become complicated when the structural analysis and fluid analysis are implemented, and Japanese Patent Application Publication No. 2000-271734 discloses the technology to implement the fluid-solidification analysis of molten metal in a mold. Problems in the above-described computational solving method have not sufficiently been solved with a simplified method, and there remains complexity in the computation and modeling when implementing the fluid-structure coupled simulation or the like.
For example, there are provided methods of simulating a fluid-structure coupled processing phenomenon in a process of liquid being applied on a film. In such phenomenon a position or shape of a surface of the film is changed by the behavior of liquid discharged and the liquid flows on this surface, and so the phenomenon progresses while both the behaviors of the film and liquid being closely related to each other. There is proposed, for example, a method in which two solvers for a fluid and structure are provided and computation progresses while exchanging information on pressure distribution and a structure position between the two solbers. Further, there is provided another method in which a coupled Jacobian matrix is prepared using a finite element method, fluid equation or structure equation and the like, and the matrix solution is obtained. Although these methods are accurate, computational load is high and a convergence computation becomes unstable in the case where film is greatly transformed or the film touches another structure.